Sumoylation, the covalent attachment of small ubiquitin-like modifier (SUMO) to cellular proteins, has emerged as an important signaling mechanism for regulating protein activity, stability/degradation, subcellular localization, and protein-protein interaction. Like ubiquitination, sumoylation is a dynamic and reversible post-translational modification that is controlled by opposing actions of sumoylating enzymes and SUMO proteases (also known as desumoylating enzymes). Sumoylation plays a critical role in regulation of numerous cellular processes, from transcriptional regulation and DNA repair to protein trafficking, mitochondrial dynamics, and apoptosis. Dysregulated sumoylation has been implicated in a variety of human diseases, including cancer, diabetes, heart disease, and neurodegenerative disorders such as Alzheimer and Parkinson diseases. Despite increasing evidence supporting the importance of sumoylation to human health and disease, our knowledge about the sumoylation/desumoylation machinery components and their cellular functions is limited. In this project, the applicant's team will use a combination of biochemical, proteomic, cell biological, and mouse genetic approaches to study a novel SUMO protease and its signaling role in cellular defense against oxidative stress and apoptosis. The results of the proposed studies should advance our knowledge of the fundamental mechanisms governing SUMO signaling in all eukaryotic cells and provide a molecular basis for understanding and treating a diverse array of human diseases that involve dysregulated sumoylation.